The posterior of the female anatomy when concerning the homosapien species. In which the diameter of the said posterior is not to exceed 50 inches but not to go below 40 inches. Equally as important the owner of the badunkadunk must possess a waist line no larger than 2/3 the diameter of the badunkadunk.

Noun: She has a nice badunkadunk
Verb: Her ass seems to be badunkadunking